Fluid handling structure and lithographic apparatus

ABSTRACT

An immersion lithographic apparatus having a fluid handling structure, the fluid handling structure configured to confine immersion fluid to a region and including: a meniscus controlling feature having an extractor exit on a surface of the fluid handling structure; and a gas knife system outwards of the extractor exit and including passages each having an exit, the passages having a plurality of first passages having a plurality of corresponding first exits on the surface, and a plurality of second passages having a plurality of corresponding second exits outwards of the first exits on the surface, wherein the surface faces and is substantially parallel to a top surface of a substrate during exposure, and the first exits and the second exits are arranged at a greater distance from the substrate than the extractor exit.

This application is a continuation of U.S. patent application Ser. No.17/186,117, filed on Feb. 26, 2021, now allowed, which is a continuationof co-pending U.S. patent application Ser. No. 16/570,382, filed on Sep.13, 2019, now U.S. Pat. No. 10,969,695, which is a continuation of U.S.patent application Ser. No. 16/063,583, filed on Jun. 18, 2018, now U.S.Pat. No. 10,416,571, which is the national phase entry of PCT patentapplication no. PCT/EP2016/080228, filed on Dec. 8, 2016, which claimsthe benefit of priority of European patent application no. 16151117.5,filed Jan. 13, 2016, of European patent application no. 16154229.5,filed on Feb. 4, 2016, and of European patent application no.16173708.5, filed on Jun. 9, 2016, each of the foregoing applications isincorporated herein in its entirety by reference.

FIELD

The present description relates to a fluid handling structure, alithographic apparatus and a method for manufacturing a device using alithographic apparatus.

BACKGROUND

A lithographic apparatus is a machine that applies a desired patternonto a substrate, usually onto a target portion of the substrate. Alithographic apparatus can be used, for example, in the manufacture ofintegrated circuits.

It has been proposed to immerse the substrate in the lithographicprojection apparatus in an immersion fluid, e.g. a liquid having arelatively high refractive index, e.g. water, so as to fill a spacebetween a final element of a projection system and the substrate. Theimmersion fluid may be distilled water, although another fluid can beused. An embodiment of the invention will be described with reference toimmersion fluid. Many fluids may be suitable, particularly a wettingfluid, an incompressible fluid and/or a fluid with higher refractiveindex than air, desirably a higher refractive index than water. Fluidsexcluding gases are particularly desirable. The point of this is toenable imaging of smaller features since the exposure radiation willhave a shorter wavelength in the fluid. (The effect of the fluid mayalso be regarded as increasing the effective numerical aperture (NA) ofthe system and also increasing the depth of focus.) Other immersionfluids have been proposed, including water with solid particles (e.g.quartz) suspended therein, or a liquid with a nano-particle suspension(e.g. particles with a maximum dimension of up to 10 nm). The suspendedparticles may or may not have a similar or the same refractive index asthe liquid in which they are suspended. Other liquids which may besuitable include a hydrocarbon, such as an aromatic, afluorohydrocarbon, and/or an aqueous solution.

In an immersion apparatus, immersion fluid is handled by an immersionsystem, device, structure or apparatus. In an embodiment the immersionsystem may supply immersion fluid and may be referred to as a fluidsupply system. In an embodiment the immersion system may at least partlyconfine immersion fluid and may be referred to as a fluid confinementsystem. In an embodiment the immersion system may provide a barrier toimmersion fluid and thereby be referred to as a barrier member, such asa fluid confinement structure. In an embodiment the immersion systemcreates or uses a flow of gas, for example to help in controlling theflow and/or the position of the immersion fluid. The flow of gas mayform a seal to confine the immersion fluid so the immersion system maycomprise a fluid handling structure, which may be referred to as a sealmember, to provide the flow of gas. In an embodiment, immersion liquidis used as the immersion fluid. In that case the immersion system may bea liquid handling system.

However, use of an immersion system may lead to defects forming on a topsurface of the substrate. Defects can be caused by a droplet ofimmersion fluid being left behind after the substrate passes under thefluid handling structure. In particular, at least two main mechanismswhich result in defects are known, which are called bulldozing and filmpulling. Defects on the surface of the substrate may lead to errors onthe surface of the substrate which can reduce yield. Defects may meanwatermarks in particular, or may mean other defects which may occur onthe surface of the substrate.

Film pulling may occur as the substrate is moved relative to animmersion system (such as the fluid handling structure or the like). Asthe surface of the substrate moves relative to the immersion fluid, anyvariation (such as an edge of the substrate) or irregularity on thesurface of the substrate may act as a meniscus pinning feature as theimmersion fluid passes over it. This means that as the fluid handlingstructure moves relative to the substrate, the meniscus of the immersionfluid between the surface of the substrate and the fluid handlingstructure is stretched. After the fluid handling structure has moved acertain distance, the meniscus will eventually break and immersion fluidis left on the surface of the substrate resulting in droplets on thesubstrate which can lead to watermark defects. The remaining dropletsmay thus lead to errors on the surface of the photosensitive materialwhich can reduce yield. Film pulling may be reduced by increasing thegas flow of a gas knife at a receding side of the fluid handlingstructure. However, this may have other consequences at an advancingside of the fluid handling structure. For example, using an increasedgas flow for the gas knife will increase “bulldozing” at the advancingside of the fluid handling structure as described below.

Bulldozing may also occur when the substrate is moved relative to thefluid handling structure. Bulldozing occurs when a droplet of immersionfluid is encountered which is ahead of the fluid handling structure. Asthe substrate moves, the advancing portion of the fluid handlingstructure collides with the droplet of immersion fluid and the dropletis pushed forwards by the fluid handling structure. As the droplet ispushed forward, defects are created on the surface of the substrate.Although this may be effectively reduced by reducing the gas flow of agas knife at the advancing side of the fluid handling structure, thismay have other consequences. For example, using a reduced gas flow forthe gas knife may mean that the confined immersion fluid is more likelyto escape from the fluid handling structure at the receding side of thefluid handling structure, thus leading to further defects.

SUMMARY

It is desirable, for example, to provide a lithographic apparatus inwhich the defects are reduced.

In the present invention, there is provided an immersion lithographicapparatus comprising a fluid handling structure, the fluid handlingstructure configured to confine immersion fluid to a region andcomprising a gas knife system, the gas knife system comprising passageseach having an exit, the passages comprising a plurality of firstpassages having a plurality of corresponding first exits, and aplurality of second passages having a plurality of corresponding secondexits, wherein at least one first passage and at least one secondpassage are configured such that the stagnation pressure of gas exitingthe first exit is greater than the stagnation pressure of gas exitingthe second exit, and the plurality of first passages and the pluralityof second passages are intermingled and arranged in a line such that thefirst exits and the second exits form a side of a shape in plan view.

In the present invention, there is provided a device manufacturingmethod comprising: projecting a patterned beam of radiation onto asubstrate, wherein the patterned beam of radiation is passed through aregion of immersion fluid; confining the immersion fluid to the regionusing a fluid handling structure, wherein the fluid handling structurecomprises a gas knife system; and generating a gas knife radiallyoutward of the region, using the gas knife system, wherein the gas knifecontributes to the confining step, and wherein the gas knife systemcomprises passages each having an exit, the passages comprising aplurality of first passages having a plurality of corresponding firstexits, and a plurality of second passages having a plurality ofcorresponding second exits, wherein at least one first passage and atleast one second passage are configured such that the stagnationpressure of gas exiting the first exit is greater than the stagnationpressure of gas exiting the second exit, and the plurality of firstpassages and the plurality of second passages are intermingled andarranged in a line such that the first exits and the second exits form aside of a shape in plan view.

In the present invention, there is provided an immersion lithographicapparatus comprising a fluid handling structure, the fluid handlingstructure configured to confine immersion fluid to a region andcomprising a gas knife in use, the fluid handling structure comprisingat least one exit, wherein the at least one exit is arranged so that thegas knife forms a side of a shape in plan view, and the at least oneexit has a geometry configured to allow movement of a droplet ofimmersion fluid from a position radially outward of the gas knife to aposition radially inward of the gas knife and configured to restrictmovement of a droplet of immersion fluid from a position radially inwardof the gas knife to a position radially outward of the gas knife.

In the present invention, there is provided an immersion lithographicapparatus comprising a fluid handling structure, the fluid handlingstructure configured to confine immersion fluid to a region andcomprising a gas knife in use, wherein the fluid handling structurecomprises at least one exit, the at least one exit being arranged so asto form the gas knife forming a side of a shape in plan view, whereinthe side comprises two end portions along that side and a gap is formedbetween the two end portions along that side of the shape in plan view,one of the end portions comprising a bend, and wherein in use, asubstrate is moved relative to the fluid handling structure in ascanning direction, and in a plane perpendicular to the scanningdirection, one of the end portions is positioned to overlap with theother end portion such that there is no gap in the plane perpendicularto scanning direction.

In the present invention, there is provided a device manufacturingmethod comprising: projecting a patterned beam of radiation onto asubstrate, wherein the patterned beam of radiation is passed through aregion of immersion fluid; confining the immersion fluid to the regionusing a fluid handling structure of an immersion system, wherein thefluid handling structure comprises a gas knife system; and generating agas knife radially outward of the region, using the gas knife system,wherein the gas knife contributes to the confining step, and the fluidhandling structure comprising at least one exit, wherein the at leastone exit is arranged so that the gas knife forms a side of a shape inplan view, and the at least one exit has a geometry configured to allowmovement of a droplet of immersion fluid from a position radiallyoutward of the gas knife to a position radially inward of the gas knifeand configured to restrict movement of a droplet of immersion fluid froma position radially inward of the gas knife to a position radiallyoutward of the gas knife.

In the present invention, there is provided a device manufacturingmethod comprising: projecting a patterned beam of radiation onto asubstrate, wherein the patterned beam of radiation is passed through aregion of immersion fluid; confining the immersion fluid to the regionusing a fluid handling structure of an immersion system, wherein thefluid handling structure comprises a gas knife system; and generating agas knife radially outward of the region, wherein the fluid handlingstructure comprises at least one exit, the at least one exit beingarranged so as to form the gas knife forming a side of a shape in planview, wherein the side comprises two end portions along that side and agap is formed between the two end portions along that side of the shapein plan view, and one of the end portions comprising a bend, and whereinin use, a substrate is moved relative to the fluid handling structure ina scanning direction, and in a plane perpendicular to the scanningdirection, one of the end portions is positioned to overlap with theother end portion such that there is no gap in the in the planeperpendicular to scanning direction.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying schematic drawings in whichcorresponding reference symbols indicate corresponding parts, and inwhich:

FIG. 1 depicts a lithographic apparatus according to an embodiment ofthe invention;

FIG. 2 depicts an immersion system for use in a lithographic projectionapparatus;

FIG. 3 depicts an embodiment of a fluid handling structure in plan view,including exits for gas forming the gas knife;

FIG. 4 depicts a cross-section through the fluid handling structure ofone of the embodiments, along the length of a portion of the gas knife;

FIG. 5 depicts a close up of a portion of FIG. 4;

FIG. 6 depicts a variation of the shape of the passage depicted in FIG.5;

FIG. 7 depicts a cross-section through the fluid handling structure ofone of the embodiments, along the length of a portion of the gas knife;

FIG. 8 depicts a close up of a portion of FIG. 7;

FIG. 9 depicts a variation of the shape of the passage depicted in FIG.8;

FIG. 10 depicts a close up of a variation of one of the passagesdepicted in FIGS. 4 to 9;

FIG. 11 depicts a cross-section through the fluid handling structure;

FIGS. 12A and 12B show a portion of the fluid handling structure in planview in accordance with one of the embodiments;

FIG. 13 depicts a close up of a variation of one of the passagesdepicted in FIGS. 12A and 12B;

FIG. 14 depicts a cross-section through the fluid handling structure;

FIG. 15 depicts a variation of the fluid handling structure depicted inFIG. 3.

DETAILED DESCRIPTION

FIG. 1 schematically depicts a lithographic apparatus according to anembodiment of the invention. The lithographic apparatus comprises:

an illuminator (otherwise referred to as an illumination system) ILconfigured to condition a projection beam B, the projection beam B beinga radiation beam (e.g. UV radiation, DUV radiation or any other suitableradiation);

a support structure (e.g. a mask support structure/mask table) MTconstructed to support a patterning device (e.g. a mask) MA andconnected to a first positioner PM configured to accurately position thepatterning device MA in accordance with certain parameters;

a support table, e.g. a sensor table to support one or more sensors,and/or a substrate table (e.g. a wafer table) WT or “substrate support”constructed to hold a substrate (e.g. a resist-coated substrate) Wconnected to a second positioning device PW configured to accuratelyposition the substrate W in accordance with certain parameters; and

a projection system (e.g. a refractive projection lens system) PSconfigured to project a pattern imparted to the projection beam B bypatterning device MA onto a target portion C (e.g. comprising one ormore dies) of the substrate W.

The illuminator IL may include various types of optical components, suchas refractive, reflective, magnetic, electromagnetic, electrostatic orother types of optical components, or any combination thereof, fordirecting, shaping, or controlling radiation.

The support structure MT supports, i.e. bears the weight of, thepatterning device MA. The support structure MT holds the patterningdevice MA in a manner that depends on the orientation of the patterningdevice MA, the design of the lithographic apparatus, and otherconditions, such as for example whether or not the patterning device MAis held in a vacuum environment. The support structure MT can usemechanical, vacuum, electrostatic or other clamping techniques to holdthe patterning device MA. The support structure MT may be a frame or atable, for example, which may be fixed or movable as required. Thesupport structure MT may ensure that the patterning device MA is at adesired position, for example with respect to the projection system PS.Any use of the terms “reticle” or “mask” herein may be consideredsynonymous with the more general term “patterning device.”

The term “patterning device” used herein should be broadly interpretedas referring to any device that can be used to impart a projection beamB with a pattern in its cross-section such as to create a pattern in atarget portion C of the substrate W. It should be noted that the patternimparted to the projection beam B may not exactly correspond to thedesired pattern in the target portion C of the substrate W, for exampleif the pattern includes phase-shifting features or so called assistfeatures. Generally, the pattern imparted to the projection beam B willcorrespond to a particular functional layer in a device being created inthe target portion C, such as an integrated circuit.

The patterning device MA may be transmissive or reflective. Examples ofpatterning devices include masks, programmable mirror arrays, andprogrammable LCD panels. Masks are well known in lithography, andinclude mask types such as binary, alternating phase-shift, andattenuated phase-shift, as well as various hybrid mask types. An exampleof a programmable mirror array employs a matrix arrangement of smallmirrors, each of which can be individually tilted so as to reflect anincoming radiation beam (e.g. a projection beam B) in differentdirections. The tilted mirrors impart a pattern in a projection beam Bwhich is reflected by the mirror matrix.

The term “projection system” used herein should be broadly interpretedas encompassing any type of projection system PS, including refractive,reflective, catadioptric, magnetic, electromagnetic and electrostaticoptical systems, or any combination thereof, as appropriate for theexposure radiation being used, or for other factors such as the use ofan immersion fluid or the use of a vacuum. Any use of the term“projection lens” herein may be considered as synonymous with the moregeneral term “projection system”.

As here depicted, the lithographic apparatus is of a transmissive type(e.g. employing a transmissive mask). Alternatively, the lithographicapparatus may be of a reflective type (e.g. employing a programmablemirror array of a type as referred to above, or employing a reflectivemask).

The lithographic apparatus may comprise a measurement table (notdepicted in FIG. 1) that is arranged to hold measurement equipment, suchas sensors to measure properties of the projection system PS. In anembodiment, the measurement table is not configured to hold a substrateW. The lithographic apparatus may be of a type having two (dual stage)or more tables (or stage or support), e.g., two or more substrate tablesWT, or a combination of one or more substrate tables WT and one or moresensor or measurement tables. In such “multiple stage” machines themultiple tables may be used in parallel, or preparatory steps may becarried out on one or more tables while one or more other tables arebeing used for exposure. The lithographic apparatus may have two or morepatterning device tables (or stages or support), e.g. two or moresupport structures MT, which may be used in parallel in a similar mannerto substrate tables WT, sensor tables and measurement tables.

Referring to FIG. 1, the illuminator IL receives a projection beam Bfrom a source SO of radiation. The source SO and the lithographicapparatus may be separate entities, for example when the source SO is anexcimer laser. In such cases, the source SO is not considered to formpart of the lithographic apparatus and the projection beam B is passedfrom the source SO to the illuminator IL with the aid of a beam deliverysystem BD comprising, for example, suitable directing mirrors and/or abeam expander. In other cases the source SO may be an integral part ofthe lithographic apparatus, for example when the source SO is a mercurylamp. The source SO and the illuminator IL, together with the beamdelivery system BD if required, may be referred to as a radiationsystem.

The illuminator IL may comprise an adjuster AD configured to adjust theangular intensity distribution of the projection beam B. Generally, atleast the outer and/or inner radial extent (commonly referred to asσ-outer and σ-inner, respectively) of the intensity distribution in apupil plane of the illuminator IL can be adjusted. In addition, theilluminator IL may comprise various other components, such as anintegrator IN and a condenser CO. The illuminator IL may be used tocondition the projection beam B, to have a desired uniformity andintensity distribution in its cross-section. Similar to the source SO,the illuminator IL may or may not be considered to form part of thelithographic apparatus. For example, the illuminator IL may be anintegral part of the lithographic apparatus or may be a separate entityfrom the lithographic apparatus. In the latter case, the lithographicapparatus may be configured to allow the illuminator IL to be mountedthereon. Optionally, the illuminator IL is detachable and may beseparately provided (for example, by the lithographic apparatusmanufacturer or another supplier).

The projection beam B is incident on the patterning device (e.g., mask)MA, which is held on the support structure (e.g., mask table) MT, and ispatterned by the patterning device MA. Having traversed the patterningdevice MA, the projection beam B passes through the projection systemPS, which focuses the projection beam B onto a target portion C of thesubstrate W. With the aid of the second positioning device PW and aposition sensor IF (e.g. an interferometric device, linear encoder orcapacitive sensor), the substrate table WT can be moved accurately, e.g.so as to position different target portions C in the path of theprojection beam B. Similarly, the first positioning device PM andanother position sensor (which is not explicitly depicted in FIG. 1) canbe used to accurately position the patterning device MA with respect tothe path of the projection beam B, e.g. after mechanical retrieval froma mask library, or during a scan.

In general, movement of the support structure MT may be realized withthe aid of a long-stroke module (coarse positioning) and a short-strokemodule (fine positioning), which both form part of the first positioningdevice PM. Similarly, movement of the substrate table WT may be realizedusing a long-stroke module and a short-stroke module, which both formpart of the second positioning device PW. The long-stroke module isarranged to move the short-stroke module over a long range with limitedprecision. The short-stroke module is arranged to move the supportstructure MT and/or substrate table WT over a short range relative tothe long-stroke module with high precision. In the case of a stepper (asopposed to a scanner) the support structure MT may be connected to ashort-stroke actuator only, or may be fixed.

Patterning device MA and substrate W may be aligned using mask alignmentmarks M1, M2 and substrate alignment marks P1, P2. Although thesubstrate alignment marks P1, P2 as illustrated occupy dedicated targetportions, they may be located in spaces between target portions C. Markslocated in spaces between the target portions C are known as scribe-lanealignment marks). Similarly, in situations in which more than one die isprovided on the patterning device MA, the mask alignment marks M1, M2may be located between the dies.

The depicted lithographic apparatus may be used to expose a substrate Win at least one of the following modes of use:

1. In step mode, the support structure MT and the substrate table WT arekept essentially stationary, while an entire pattern imparted to theprojection beam B is projected onto a target portion C at one time (i.e.a single static exposure). The substrate table WT is then shifted in theX direction and/or Y direction (i.e. a stepping direction) so that adifferent target portion C can be exposed. In step mode, the maximumsize of the exposure field limits the size of the target portion Cimaged in a single static exposure.

2. In scan mode, the support structure MT and the substrate table WT arescanned synchronously while a pattern imparted to the projection beam Bis projected onto a target portion C (i.e. a single dynamic exposure).The velocity and direction of the substrate table WT relative to thesupport structure MT may be determined by the (de-)magnification andimage reversal characteristics of the projection system PS. In scanmode, the maximum size of the exposure field limits the width (in anon-scanning direction) of the target portion C in a single dynamicexposure, whereas the length of the scanning motion determines theheight (in a scanning direction) of the target portion C.

3. In another mode, the support structure MT is kept essentiallystationary holding a programmable patterning device, and the substratetable WT is moved or scanned while a pattern imparted to the projectionbeam B is projected onto a target portion C. In this mode, generally apulsed radiation source is employed as the source SO and theprogrammable patterning device is updated as required after eachmovement of the substrate table WT or in between successive radiationpulses during a scan. This mode of operation can be readily applied tomaskless lithography that utilizes a programmable patterning device,such as a programmable mirror array of a type as referred to above.

Combinations and/or variations on the above described modes of use orentirely different modes of use may also be employed.

Arrangements for providing fluid between a final element of theprojection system PS and the substrate W can be classed into threegeneral categories of immersion system. These include a bath typearrangement, a localized immersion system and an all-wet immersionsystem. The present invention relates to the use of a localizedimmersion system.

The localized immersion system uses a fluid supply system in which fluidis only provided to a localized area of the substrate W. The area filledby fluid is smaller in plan than the top surface of the substrate W andthe area filled with fluid remains substantially stationary relative tothe projection system PS while the substrate W moves underneath thatarea. A meniscus controlling feature can be present to seal fluid to thelocalized area. One way which has been proposed to arrange for this isdisclosed in PCT patent application publication no. WO 99/49504. Themeniscus controlling feature may be a meniscus pinning feature.

FIG. 2 schematically depicts an immersion system (which can otherwise bereferred to as a localized fluid supply system or fluid handling system)with a fluid handling structure 12 (which could also be referred to as afluid confinement structure), which extends along at least a part of aboundary of a space 11 between a final element of the projection systemPS and the substrate table WT or substrate W. Reference in the followingtext to surface of the substrate W also refers in addition or in thealternative to a surface of the substrate table WT, unless expresslystated otherwise. In an embodiment, a seal is formed between the fluidhandling structure 12 and the surface of the substrate W and which maybe a contactless seal such as a gas seal 16 (such a system with a gasseal is disclosed in European patent application publication no. EP1,420,298). The seal can be provided by a meniscus controlling feature.

The fluid handling structure 12, for example as depicted in FIG. 2, atleast partly confines fluid in the space 11 (which may otherwise bereferred to as a region) between the final element of the projectionsystem PS and the substrate W. The space 11 is at least partly formed bythe fluid handling structure 12 positioned below and surrounding thefinal element of the projection system PS. Fluid is brought into thespace 11 below the projection system PS and within the fluid handlingstructure 12 by opening 13. The fluid may be removed by opening 13.Whether fluid is brought into the space 11 or removed from the space 11by the opening 13 may depend on the direction of movement of thesubstrate W and substrate table WT.

The fluid may be confined in the space 11 by the gas seal 16 which,during use, is formed between the bottom of the fluid handling structure12 and the surface of the substrate W. As depicted in FIG. 3, a meniscus320 is at the edge of the immersion fluid beneath the fluid handlingstructure 12. A further meniscus 400 is between the top of the fluidhandling structure 12 and the final element of the projection system PS.The gas in the gas seal 16 is provided under pressure via inlet 15 tothe gap between the fluid handling structure 12 and substrate W. The gasis extracted via a channel associated with outlet 14. The overpressureon the gas inlet 15, vacuum level on the outlet 14 and geometry of thegap are arranged so that there is a high-velocity gas flow inwardly thatconfines the fluid. The force of the gas on the fluid between the fluidhandling structure 12 and the substrate W confines the fluid in thespace 11. Such a system is disclosed in United States patent applicationpublication no. US 2004-0207824, which is hereby incorporated byreference in its entirety.

FIG. 3 illustrates schematically and in plan meniscus controllingfeatures of an immersion system including a fluid handling structure 12which may have outlets using the gas drag principle and to which anembodiment of the present invention may relate. The features of ameniscus controlling feature are illustrated which may, for example,replace the meniscus controlling features depicted by the gas seal 16,provided by the inlet 15 and the outlet 14 in FIG. 2. The meniscuscontrolling feature of FIG. 3 is a form of extractor, for example a dualphase extractor. The meniscus controlling feature comprises a pluralityof discrete openings 50. Each opening 50 is illustrated as beingcircular, though this is not necessarily the case. Indeed, the shape isnot essential and one or more of the openings 50 may be one or moreselected from: circular, elliptical, rectilinear (e.g. square, orrectangular), triangular, etc. and one or more openings may be elongate.

There may be no meniscus controlling features radially inwardly of theopenings 50. The meniscus 320 is pinned between the openings 50 withdrag forces induced by gas flow into the openings 50. A gas dragvelocity of greater than about 15 m/s, desirably about 20 m/s issufficient. The amount of evaporation of fluid from the substrate W maybe reduced, thereby reducing both splashing of fluid as well as thermalexpansion/contraction effects.

Various geometries of the bottom of the fluid handling structure arepossible. For example, any of the structures disclosed in U.S. patentapplication publication no. US 2004-0207824 or U.S. patent applicationpublication no. US 2010-0313974 could be used in an embodiment of thepresent invention. An embodiment of the invention may be applied to afluid handling structure 12 which has any shape in plan, or has acomponent such as the outlets are arranged in any shape. Such a shape ina non-limiting list may include an ellipse such as a circle, arectilinear shape such as a rectangle, e.g. a square, or a parallelogramsuch as a rhombus or a cornered shape with more than four corners suchas a four or more pointed star, for example, as depicted in FIG. 3.

Known lithographic apparatus may comprise a fluid handling structure 12comprising a gas knife. The gas knife can be used to help confineimmersion fluid to the space 11. Therefore, the gas knife can be usefulin preventing immersion fluid from escaping from the space 11, whichcould later lead to defects. Providing a strong gas knife is useful inpreventing film pulling because a strong gas knife will reduce orprevent the amount of immersion fluid which is dragged behind the fluidhandling structure 12, and may break up the film faster to reduce theamount of immersion fluid left behind the fluid handling structure 12.However, when the gas knife is strong, this may make defects on theadvancing side of the gas knife worse, because as the gas knife collideswith droplets of immersion fluid on the surface of the substrate W, astrong gas knife will not allow immersion fluid droplets to pass inwardsof the gas knife. This means that the droplets of immersion fluid willbe pushed forwards by the advancing side of the fluid handling structure12 which can lead to bulldozing. As film pulling and bulldozing bothcause defects which increase errors and possibly reduce yield, it isbeneficial to provide a fluid handling structure 12 which addresses bothof these issues simultaneously.

In the present invention an immersion lithographic apparatus is providedwhich comprises a fluid handling structure 12. The fluid handlingstructure 12 may be as described above, for example in relation to FIG.3. The fluid handling structure 12 is configured to confine immersionfluid to a region and comprises a gas knife system. The gas knife systemmay be configured to generate a gas knife in use. The gas knife may beradially outward of the space 11 (otherwise referred to as the region)and may contribute to confining the immersion fluid. The gas knifesystem comprises passages each having an exit 60. The gas knife may beformed by gas exiting the exits 60 in use. The exits 60 form at leastone side of a shape in plan view. The exits 60 may form at least one,multiple or all the sides of the shape in plan view. For example, theexits 60 may form the sides of a four pointed star as shown in FIG. 3.The shape may have a plurality of sides, for example any appropriatenumber of sides may be provided, e.g. 3, 4, 5, 6, 7, 8, 9, 10 or more.As described above, the exits 60 may form the sides of any shape andthis is not particularly limiting. FIG. 3 depicts the scanning direction110 as in-line with two of the points of the four point star but thismay not be the case. The shape formed by the gas knife may be alignedwith the scanning direction 110 in any selected orientation. As depictedin FIG. 4, the passages comprises a plurality of first passages 70 ahaving a plurality of corresponding first exits 60 a, and a plurality ofsecond passages 70 b having a plurality of corresponding second exits 60b. The gas knife is formed in use by gas exiting the first exits 60 aand the second exits 60 b.

In a first embodiment, the at least one first passage 70 a and the atleast one second passage 70 b are configured such that the stagnationpressure of gas exiting the first exit 60 a is greater than thestagnation pressure of gas exiting the second exit 60 b. The stagnationpressure is the pressure that would be reached if an isentropic processwere used to bring a fluid to rest. In other words, the stagnationpressure is the pressure at a stagnation point in a fluid where thefluid velocity is zero and all kinetic energy has been converted topressure by an adiabatic, reversible (i.e. isentropic) process. Thedifferent stagnation pressure means that when in use, the stagnationpressure of the gas knife on the substrate W varies such that it isgreater in areas with gas supplied by the first exit 60 a and less inareas supplied by the second exit 60 b. This correlates to having“strong jets” in the gas knife which are useful for creating de-wettingpoints to break the film to reduce film pulling and “soft jets” toreduce bulldozing.

For previously known apparatus, it is known that increasing thestagnation pressure of the gas knife may reduce the film pulling at thereceding side of the fluid handling structure 12, however, this can havean adverse effect on bulldozing at the advancing side of the fluidhandling structure 12. Therefore, increase of the stagnation pressure ofthe gas knife may be limited and a balance of higher stagnation pressureand lower stagnation pressure needs to be reached. The principle of thepresent invention relates to having a mix of higher stagnation pressurepoints and lower stagnation pressure points along one side of the fluidhandling structure 12, and the mix of higher and lower stagnationpressures has a different effect depending on whether it is on anadvancing or receding side. Providing the “soft jets” (i.e. lowstagnation pressure) may reduce the bulldozing at the advancing side ofthe fluid handling structure 12 because when bulldozing does occur, somedroplets of immersion fluid may move radially inward of the gas knifedue to the “soft jets”. In known apparatus which has uniform gas flowand velocity, to reduce bulldozing effects at the advancing side of afluid handling structure, it is necessary to reduce the gas flow fromthe gas knife everywhere. However, reducing the stagnation pressure ofthe gas can increase film pulling at the receding side. However, in thepresent invention, film pulling will not be negatively affected by thereduced stagnation pressure due to the presence of the “strong jets”(i.e. high stagnation pressure). In other words, in the presentinvention, the stagnation pressure is lower for the “soft jets” whichreduces bulldozing, but the film pulling is improved using “strong jets”compared to known apparatus which would require the stagnation pressureof the whole gas knife to be reduced everywhere.

The plurality of first exits 60 a and the plurality of second exits 60 bmay be intermingled and arranged in a line. This means that along a lineof exits, i.e. along the gas knife, there may be some first exits 60 aand some second exits 60 b. Thus, the gas knife is formed of strong jetsand soft jets. As described later, this may be in a repeating and/oruniform pattern (e.g. alternating first exits 60 a and second exits 60b). The plurality of first exits 60 a and second exits 60 b form atleast one side of the shape in plan view as described above. The atleast one first passage 70 a could mean one or plural, possibly meaningall, for example all of the first passages 70 a each having the shapedescribed. The same applies to the at least one second passage 70 b.

Alternatively, in the embodiment, the velocity (v) of the gas exitingthe first exit 60 a and the gas exiting the second exit 60 b may becompared, i.e. the velocity may be referred to rather than thestagnation pressure. The velocity is the exit velocity of the gasexiting the first gas exit 60 a at the first gas exit 60 a and/or thesecond gas exit 60 b at the second gas exit 60 b respectively. Thestagnation pressure is related to the velocity of the gas exiting eitherof the first exit 60 a and the second exit 60 b. An increase in thestagnation pressure corresponds to an increase in ρv², wherein ρ is thedensity of the gas exiting the first exit 60 a and the second exit 60 b.Thus, changes in the stagnation pressure are relatable to changes in thevelocity, and the velocity may be used as a parameter of gas exiting thefirst exit 60 a and the second exit 60 b as described in the embodimentbelow. It will be understood that a conversion of values would be neededbut that the principles remain the same.

There may be any number of first passages 70 a and second passages 70 b,and the first exits 60 a and the second exits 60 b may be formed of avariety of shapes, e.g. discrete circular holes, or holes of othershape, or slits, etc.

The gas knife is formed in use by gas exiting the first exits 60 a andthe second exits 60 b. In other words, the gas knife is formed in use bygas exiting both of the first exits 60 a and the second exits 60 b. Inthis way, the gas knife is formed have a stagnation pressure profile,and the stagnation pressure profile along the gas knife varies dependingon whether the gas at any particular point along the gas knife exited afirst exit 60 a or a second exit 60 b.

This means that the gas knife is formed from gas exiting the first exits60 a and the second exits 60 b, which means that the gas forming the gasknife is at different stagnation pressures depending on which passagethe gas passes through. As such, the stagnation pressure profile of thegas knife is not the same along the length of the gas knife.

At the second exits 60 b, the gas exits at a lower stagnation pressure(i.e. the soft jets) which means that droplets of immersion fluid whichare present on the surface of the substrate W may be able to passthrough, for example, at the advancing side of the fluid handlingstructure 12. Therefore, droplets of immersion fluid which collide withthe gas knife can pass through and may enter into the space 11. This mayreduce or prevent the number of droplets which are pushed along thesurface of the substrate W causing a watermark.

At the first exits 60 a, the gas exits at a higher stagnation pressure(i.e. the strong jets), which means that the gas may form discretepoints of high stagnation pressure. The higher stagnation pressure areasof the gas knife may break up a film, for example, at the receding sideof the fluid handling structure 12, which has formed due to filmpulling. In other words, these discrete points of higher pressurepenetrates the film of the immersion fluid below. This means that theextent to which immersion fluid is pulled along the surface of thesubstrate W at the receding side of the fluid handling structure 12 maybe reduced or prevented which may reduce or prevent immersion fluidbeing left behind as the surface of the substrate W passes under thefluid handling structure 12 and may also reduce the thickness of thefilm on the surface of the substrate W. Thus forming the gas knife fromfirst exits 60 a and second exits 60 b from which gas exits at differentstagnation pressures may reduce or prevent film pulling and/orbulldozing, depending on the location of the immersion fluid withrespect to the fluid handling structure 12, i.e., whether the side isthe advancing side or the receding side of the fluid handling structure12.

The stagnation pressure of gas exiting the second exit 60 b maypreferably be approximately greater than or equal to 5 mbars, orpreferably approximately greater than or equal to 10 mbars. Thestagnation pressure of gas exiting the second exit 60 b may preferablybe approximately less than or equal to 500 mbars, or preferablyapproximately less than or equal to 400 mbars. The stagnation pressureof gas exiting the second exit 60 b may preferably be approximatelybetween 5 mbars and 500 mbars, or more preferably approximately between10 mbars to 400 mbars. The stagnation pressure of gas exiting the firstexit 60 a may preferably be approximately greater than or equal to 40mbars, or preferably approximately greater than or equal to 100 mbars.The stagnation pressure of gas exiting the first exit 60 a maypreferably be approximately less than or equal to 500 mbars, orpreferably approximately less than or equal to 400 mbars. The stagnationpressure of gas exiting the first exit 60 a may preferably beapproximately between 40 mbars and 500 mbars or more preferablyapproximately between 100 mbars to 400 mbars.

The at least one first passage 70 a may have a first entrance 65 a andthe at least one second passage 70 b may have a second entrance 65 b.There may be a corresponding entrance for every exit. Thus, the firstpassage 70 a may have a corresponding first entrance 65 a and first exit60 a and the second passage 70 b may have a corresponding secondentrance 65 b and second exit 60 b. The first passage 70 a may have morethan one entrance or exit. The second passage 70 b may have more thanone entrance or exit.

The pitch between the first passage 70 a and the second passage 70 b maybe determined as the distance from a center of the cross-sectional areaof the first entrance 65 a to a center of the cross-sectional area ofthe second entrance 65 b. As described below, if different patterns offirst passage 70 a and second passages 70 b are used, the pitch isdetermined as the distance between the centers of the cross-sectionalarea of adjacent entrances. The pitch may preferably be greater than orequal to approximately 100 μm, or more preferably, approximately 200 μm.The pitch may preferably be less than or equal to approximately 1000 μm,or preferably approximately 500 μm, or more preferably, approximately400 μm. The pitch may preferably be between approximately 100 μm to 1000μm, or preferably between approximately 100 μm to 500 μm, or morepreferably, the pitch may be between approximately 200 μm to 400 μm.

There are different ways in which the stagnation pressure at thedifferent exits 60 a, 60 b may be varied. For example, the first passage70 a and second passage 70 b may be connected to different gas sourceshaving different flow rates, e.g. that at least one first passage 70 amay be connected to a first gas source and the at least one secondpassage 70 b may be connected to a second gas source. There may befurther methods of providing gas from the second exit 60 b at a reducedstagnation pressure compared to the gas exiting the first exit 60 a. Forexample, the first passage 70 a and/or the second passage 70 b maycomprise a variable or fixed restrictor which allows the amount of flow,and thus the stagnation pressure may be controlled in the first passage70 a and/or the second passage 70 b.

A specific arrangement is described in a second embodiment below. Thesecond embodiment may be the same as the first embodiment except asherein described. In the second embodiment, the shape of the firstpassage 70 a and the shape of the second passage 70 b can be configuredsuch that the stagnation pressure of gas exiting the first exit 60 a isgreater than the stagnation pressure of gas exiting the second exit 60b. This may optionally be in addition to the ways of varying thestagnation pressure at different exits 60 a and 60 b already describedin the first embodiment, or may be as an alternative. Although variousdifferent sized passages may be used, the cross-sectional areas of eachof the first entrance 65 a, first exit 60 a, second entrance 65 b andsecond exit 60 b may be selected in order to control the stagnationpressure of gas exiting the first passage 70 a relative to thestagnation pressure of gas exiting the second passage 70 b. Therefore,the sizes of these cross-sectional areas may have some which are thesame as each other, or may all be different from each other.

In the second embodiment, a first ratio is the ratio of the first exitto the first entrance, and a second ratio is the ratio of the secondexit to the second entrance. The stagnation pressure at the differentexits may be controlled by controlling the first ratio relative to thesecond ratio. In this embodiment, the second ratio is larger than thefirst ratio. This means that the proportional difference in area betweenthe second exit 60 b compared to the second entrance 65 b is bigger thanthe proportional difference in area between the first exit 60 a and thefirst entrance 65 a. As will be clear from the description below, thismay include variations wherein the cross-sectional area of the secondexit 60 b and the second entrance 65 b is substantially constant orwherein the cross-sectional area between the first exit 60 a and thefirst entrance 65 a is substantially constant.

The cross-sectional area of the first entrance 65 a, first exit 60 a,second entrance 65 b and second exit 60 b may be any size within reason,as long as the sizes are chosen relative to each other to produce thestagnation pressure variation described above. For example, the diameterof at least one of the first entrance 65 a, first exit 60 a, secondentrance 65 b and/or second exit 60 b may be greater than or equal toapproximately 50 μm, or more preferably approximately 70 μm. Thediameter of at least one of the first entrance 65 a, first exit 60 a,second entrance 65 b and/or second exit 60 b may be less than or equalto approximately 300 μm, or more preferably approximately 200 μm. Thediameter of at least one of the first entrance 65 a, first exit 60 a,second entrance 65 b and/or second exit 60 b may be betweenapproximately 50 μm to 300 μm, or more preferably between approximately70 μm to 200 μm.

In an embodiment, the cross-sectional area of first exit 65 a isapproximately equal to or less than the cross-sectional area of thefirst entrance 60 a and the cross-sectional area of the second exit 65 bis approximately equal to larger than the cross-sectional area of thesecond entrance 60 b. As the second ratio is larger than the firstratio, this means that the first passage 70 a may decrease incross-sectional area from the first entrance 60 a to the first exit 65 aand the second passage 70 b may have substantially the samecross-sectional area of the second entrance 60 b and the second exit 65b, or the second passage 70 b may increase in cross-sectional area fromthe second entrance 60 b to the second exit 65 b, or the cross-sectionalarea of the first entrance 60 a and the first exit 60 b is substantiallythe same and the second passage 70 b may increase in cross-sectionalarea from the second entrance 60 b to the second exit 65 b.

In the second embodiment, each of the first passages 70 a has the firstentrance 65 a and each of the second passages 70 b has the secondentrance 65 b and the first exit 60 a has approximately the samecross-sectional area as the first entrance 65 a and the second exit 60 bhas a larger cross-sectional area than the second entrance 65 b. Theexits 60 depicted in FIG. 3 may have varying exit sizes, as describedsuch that the stagnation pressure of gas forming the gas knife via thefirst exits 60 a is at a different stagnation pressure to gas formingthe gas knife via the second exits 60 b. As will be seen from FIG. 4,gas flow through the second passages 70 b is expanded as it approachesthe second exits 60 b, which may thus decrease the stagnation pressureof the gas as it exits the second exits 60 b to form the gas knife. FIG.4 depicts a cross-section of the fluid handling structure 12 along thelength of a portion of the gas knife.

The first entrances 65 a and the second entrances 65 b are in fluidcommunication with a common manifold and/or are connected to a commongas source. For example, a gas source 75 may provide gas to the firstentrances 65 a and the second entrances 65 b.

The second embodiment is depicted in FIG. 4. FIG. 4 depicts two firstpassages 70 a and two second passages 70 b. The number of each of thepassages may be much higher.

In this embodiment, the shape and variation of the passages may beformed in many different ways in order to control the relativestagnation pressure of gas exiting the first exit 60 a and the secondexit 60 b. The shape of the passages may affect the gas exiting the gasexits 60, and the internal shape of the passages can be selected toachieve the desired stagnation pressure, or ratio of stagnationpressures between gas exiting the first exit 60 a and the second exit 60b.

For example, the second passage 70 b may increase in cross-sectionalarea for the whole length of the second passage 70 b. The second passage70 b may stay the same or increase in cross-sectional area for the wholelength of the second passage 70 b. In other words, the cross-sectionalarea of the second passage 70 b may increase monotonically from thesecond entrance 65 b to the second exit 60 b. The cross-sectional areaof the second passage 70 b may increase linearly with the distance fromthe second entrance 65 b or proportionally to a higher power of thatdistance. For example, the diameter of the second passage 70 b mayincrease linearly, as depicted in FIGS. 4 and 5. The second passage 70 bmay form a frustum shape from the second entrance 65 b to the secondexit 60 b.

It may be useful to control the increase in cross-sectional area toavoid gas passing through the second passage 70 b from detaching fromwalls 71 b (which may otherwise be referred to as the sides) of thesecond passage 70 b. The flow of gas passing through the first passage70 a and the second passage 70 b may be laminar. Controlling thevariation of the cross-sectional area may prevent detachment of thelaminar gas flow from the walls 71 b of the second passage 70 b.Detachment of the flow of gas may result in turbulence and loss ofefficiency of the gas knife.

Detachment may be reduced or avoided by maintaining the walls 71 b ofthe second passage 70 b within a preferred angular range. A close up oneof the second passages 70 b of FIG. 4 is depicted in FIG. 5. As shown,the second passage 70 b may have a second major axis SMA. The secondmajor axis SMA may pass through the center of the cross-sectional areaof the second entrance 65 b and the center of the cross-sectional areaof the second exit 60 b. The angle θ of the walls 71 b of the secondpassage 70 b may be determined relative to the second major axis SMAthrough the second passage 70 b. The angle θ of sides of the secondpassage 70 b to the second major axis SMA may preferably be betweenapproximately 0.5° and 7°. The angle may be selected to control thestagnation pressure profile of gas exiting the second gas exit 60 b.Known techniques of manufacture may be used to create passages withangles of this size, for example, by using ablation technology orElectrical Discharge Machining (EDM).

Alternatively, instead of the cross-sectional area increasing along thelength of the second passage 70 b (albeit at a constant or varied rate),the second passage 70 b may be formed of portions of passage havingconstant cross-sectional area as depicted in FIG. 6. For example, thesecond passage 70 b may comprise a first portion 72 b having asubstantially uniform cross-sectional area along the length of the firstportion 72 b, and a second portion 73 b having a substantially uniformcross-sectional area along the length of the second portion 73 b. Thesecond portion 73 b may have a larger cross-sectional area than thefirst portion 73 a. As shown in FIG. 6, this results in a step shapebetween the first portion 72 b and the second portion 73 b.

The second passage 70 b may in fact be separated into several smallportions, each with a constant cross-sectional area. Although FIG. 6 isdepicted with only two portions, any number of portions may be used, aslong as the shape of the portions result in the stagnation pressure ofgas exiting the second exit 60 b to be lower than gas exiting the firstexit 60 a. For example, as described above, this may mean that theportions increase in cross-sectional area from the second entrance 65 bto the second exit 60 b. The transitions between portions of constantcross-section may be more gradual than depicted in FIG. 6.

A specific arrangement is described in a third embodiment below. Thethird embodiment may be the same as the first embodiment except asherein described. In the third embodiment, the shape of the firstpassage 70 a and the shape of the second passage 70 b can be configuredsuch that the stagnation pressure of gas exiting the first exit 60 a isgreater than the stagnation pressure of gas exiting the second exit 60b. This may optionally be in addition to the ways of varying thestagnation pressure at different exits 60 a and 60 b already describedin the first embodiment, or may be as an alternative. Each of the firstpassages 70 a has a first entrance 65 a and each of the second passages70 b has a second entrance 65 b and the first entrance 65 a has a largercross-sectional area than the first exit 60 a and the second exit 60 bhas approximately the same cross-sectional area as the second entrance65 b. Essentially, this may result in the same stagnation pressuredifference between gas exiting the first gas exit 60 a and the secondgas exit 60 b as described above in the second embodiment. However, inthis instance, gas flow through the first passage 70 a is confined (e.g.restricted) as it approaches the first exit 60 a, which may thusincrease the stagnation pressure of the gas as it exits the first exit60 a to form the gas knife.

The first entrances 65 a and the second entrances 65 b are in fluidcommunication with a common manifold and/or are connected to a commongas source. For example, a gas source 75 may provide gas to the firstentrances 65 a and the second entrances 65 b.

The third embodiment is depicted in FIG. 7. FIG. 7 depicts across-section of the fluid handling structure 12 along the length of aportion of the gas knife. FIG. 7 depicts two first passages 70 a and twosecond passages 70 b. The number of each of the passages 70 may be muchhigher.

In this embodiment, the shape and variation of the passages may beformed in many different ways in order to control the relativestagnation pressure of gas exiting the first exit 60 a and the secondexit 60 b. The shape of the passages may affect the gas exiting the gasexits 60, and the internal shape of the passages can be selected toachieve the desired stagnation pressure, or ratio of stagnationpressures between gas exiting the first exit 60 a and the second exit 60b.

For example, the first passage 70 a may decrease in cross-sectional areafor the whole length of the first passage 70 a. The cross-sectional areaof the first passage 70 a may stay the same or decrease incross-sectional area along the whole length of the first passage 70 a.In other words, the cross-sectional area of the first passage 70 a maydecrease monotonically from the first entrance 65 a to the first exit 60a. The cross-sectional area of the first passage 70 a may decreaselinearly with the distance from the first entrance 65 a orproportionally to a higher power of that distance. For example, thediameter of the first passage 70 a may decrease linearly, as depicted inFIG. 7. The first passage 70 a may form a frustum shape from the firstentrance 65 a to the first exit 60 a.

It may be useful to control the decrease in cross-sectional area toavoid gas passing through the first passage 70 a from detaching fromwalls (which may otherwise be referred to as the sides) of the firstpassage 70 a. The gas passing through the first passage 70 a and thesecond passage 70 b may be laminar. Controlling the variation of thecross-sectional area may prevent detachment of the laminar gas flow fromthe walls 74 a of the first passage 70 a. Detachment of the flow of gasmay result in turbulence and loss of efficiency of the gas knife.

Detachment may be reduced or avoided by maintaining the walls 74 a ofthe first passage 70 a within a preferred angular range. A close up ofone of the first passages 70 a of FIG. 7 is depicted in FIG. 8. Asshown, the first passage 70 a may have a first major axis FMA, asdepicted in FIG. 8. The first major axis FMA may pass through the centerof the cross-sectional area of the first entrance 65 a and the center ofthe cross-sectional area of the first exit 60 a. The angle θ of thewalls 74 a of the first passage 70 a may be determined relative to thefirst major axis FMA through the first passage 70 a. This may bedetermined in a similar way to as depicted in FIG. 5 for the secondembodiment. The angle θ of the sides of the first passage 70 a to thefirst major axis FMA may preferably be greater than or equal toapproximately 0.5°. The angle θ may preferably be less than or equal toapproximately 30°, or more preferably, less than or equal toapproximately 10°. The angle θ may preferably be between approximately0.5° and 30°, or more preferably, the angle θ may be betweenapproximately 0.5° and 10°. The angle may be selected to control thestagnation pressure profile of gas exiting the first gas exit 60 a.Known techniques of manufacture may be used to create passages withangles of this size, for example, by using ablation technology orElectrical Discharge Machining (EDM).

Alternatively, instead of the cross-sectional area decreasing along thelength of the first passage 70 a (albeit at a constant or varied rate),the first passage 70 a may be formed of portions of passage havingconstant cross-sectional area, as depicted in FIG. 9. This is similar tothe variations depicted for FIG. 6 for the second embodiment, exceptthat in the present embodiment, the first passage 70 a decreases in sizefrom the first entrance 65 a to the first exit 60 a. For example, thefirst passage 70 a may comprise a first portion having a substantiallyuniform cross-sectional area along the length of the first portion, anda second portion having a substantially uniform cross-sectional areaalong the length of the second portion. The second portion may have asmaller cross-sectional area than the first portion. As shown in FIG. 9,this results in a step shape between the first portion and the secondportion.

The first passage 70 a may be separated into several small portions,each with a constant cross-sectional area. Although FIG. 9 is depictedwith only two portions, any number of portions may be used, as long asthe shape of the portions result in the stagnation pressure of gasexiting the second exit 60 b to be lower than gas exiting the first exit60 a. For example, as described above, this may mean that the portionsdecrease in cross-sectional area from the first entrance 65 a to thefirst exit 60 a. The transitions between portions of constantcross-section may be more gradual than depicted in FIG. 9.

In a fourth embodiment, the second passage 70 b may vary as described inrelation to the second embodiment, and the first passage 70 a may varyas described in relation to the third embodiment.

Providing strong and soft jets, i.e. using first exits 60 a and secondexits 60 b as described in relation to any of the first to fourthembodiments may allow movement of a droplet of immersion fluid from aposition radially outward of the gas knife to a position radially inwardof the gas knife and may restrict movement of a droplet of immersionfluid from a position radially inward of the gas knife to a positionradially outward. In other words, the shape of at least one firstpassage 70 a and the shape of the at least one second passage 70 b maybe configured to allow movement of a droplet of immersion fluid from aposition radially outward of the gas knife to a position radially inwardof the gas knife, and configured to restrict movement of a droplet ofimmersion fluid from a position radially inward of the gas knife to aposition radially outward of the gas knife. Thus, the gas knife formedby first exits 60 a and second exits 60 b may have the same advantagesas described in relation to the at least one exit 200 provided in thefurther embodiment described below. Particularly, at the advancing sideof the fluid handling structure 12, immersion fluid may be allowed tomove from a position radially outward of the gas knife to a positionradially inward of the gas knife as fluid may pass through the soft jetsand at the receding side of the fluid handling structure 12, the strongjets may restrict movement of the immersion fluid from a positionradially inward to a position radially outward. The strong jets mayreduce film pulling, as described above, compared to if a gas knife in aknown apparatus at a lower stagnation pressure without a mix of higherand lower stagnation pressures were used.

In any of the above embodiments, the shape of the first passage 70 a andthe second passage 70 b is not particularly limiting and these passagescan be any shape. For example, at least one of the first entrance 65 a,first exit 60 a, second entrance 65 b and/or second exit 60 b may beapproximately circular in cross-section. Providing a circular shapethroughout the first passage 70 a and/or the second passage 70 b mayhelp reduce or prevent detachment of gas flow from the sides of thefirst passage 70 a and/or second passage 70 b respectively.

In any of the above embodiments, the first passage 70 a and the secondpassage 70 b may be alternating. In other words, there may be a firstpassage 70 a between two second passages 70 b and vice versa.Alternatively, the first passages 70 a and the second passages 70 b maybe provided in a repeating pattern. For example, a single first passage70 a may be provided followed by two second passages 70 b, or threesecond passages 70 b, or four second passages 70 b and so on, and viceversa. There may be any number of first passages 70 a followed by anynumber of second passages 70 b. The number of first passages 70 a andsecond passages 70 b may be the same, for example, there may be onefirst passage 70 a followed by one second passage 70 b, or two firstpassages 70 a followed by two second passages 70 b, or three firstpassages 70 a followed by three second passages 70 b and so on. Thenumber of each type of passage may not be the same, for example, theremay be two first passages 70 a followed by three second passages 70 band so on. The pattern of first passages 70 a and second passages 70 bmay be arranged in a desired manner to provide a desired stagnationpressure variation along the length of the gas knife.

As described above, immersion fluid may be left behind after the fluidhandling structure 12 is moved relative to the substrate W. Althoughvarying the stagnation pressure profile of the gas knife as describedabove may help reduce the immersion fluid left behind, it may bepossible to reduce this further by considering the shear stress exertedon the surface of the immersion fluid.

In any of the above embodiments, the first exit 60 a and the second exit60 b are located on a surface 80 of the fluid handling structure 12. Thesurface 80 may be facing and substantially parallel to a top surface 90of a substrate W when in use. As described above and as depicted in FIG.7, the first passage 70 a may have a first major axis FMA which passesthrough the center of the cross-sectional area of the first entrance 65a and first exit 60 a and the second passage 70 b may have a secondmajor axis SMA which passes through the center of the cross-sectionalarea of the second entrance 65 b and second exit 60 b. The first majoraxis FMA and/or the second major axis SMA may be at an angle to the topsurface 90 of the substrate W when in use. This is depicted with respectto the first major axis FMA in FIG. 10. In other words, the firstpassage 70 a and/or the second passage 70 b may be at an incline. Theangle α may preferably be greater than or equal to approximately 10°, ormore preferably approximately 30°. The angle α may preferably be lessthan or equal to approximately 75°, or more preferably approximately60°. The angle α may preferably be between approximately 10° to 75°, ormore preferably between approximately 30° to 60°.

By providing the first passage 70 a and/or the second passage 70 b at anincline, the shear stress on the surface of the immersion fluid mayincrease and there may be an inflow underneath the first exit 60 aand/or the second exit 60 b. This inflow may have an inward shear stress(possibly a large inward shear stress) which may help droplets ofimmersion fluid to pass radially inward in the fluid handling structure12 whilst maintaining the immersion fluid radially inward of the gasknife when in use, i.e. confining the immersion fluid inside the space11.

In any of the above embodiments, the fluid handling structure 12 mayfurther comprise a fluid extractor radially inward of the gas knife. Thefluid extractor may have at least one extractor exit 85. The fluidextractor may be the same as the extractor described in relation to FIG.3 and the extractor exit 85 may correspond to the openings 50. Theextractor exit 85 may be on the same surface 80 of the fluid handlingstructure 12 as the first exit 60 a and the second exit 60 b. Being onthe same surface means that the extractor exit 85 and the first exit 60a and/or the second exit 60 b are both on the same side of the fluidhandling structure 12, for example, a side of the fluid handlingstructure 12 facing the top surface 90 of the substrate Win use. Thesurface 80 may have variations in height as described below. The surface80 may connect the extractor exit 85 and the first exit 60 a and/or thesecond exit 60 b, for example as a physical part of the fluid handlingstructure 12 between them. The surface 80 of the fluid handlingstructure 12 may be facing and substantially parallel to the top surface90 of the substrate W when in use. There may be a step in the surface 80such that the first exit 60 a and the second exit 60 b are at a greaterdistance from the substrate W than the extractor exit 85 when in use,i.e. the gas knife is elevated. An example is depicted in FIG. 11 whichshows a cross section through the extractor exit 85 and one of the firstpassages 70 a. Different cross sections taken at different points alongthe length of the gas knife may depict the second passage 70 b insteadof the first passage 70 a.

The step may be a vertical step, as depicted in FIG. 11, or it may beangled, i.e. the difference between the parts of the surface 80 at adifferent height may be angled, i.e. inclined. Alternatively, the stepmay be curved. Varying the height of the first exit 60 a and the secondexit 60 b may alter the effect of the resulting gas knife on the surfaceof the substrate W and may help reduce defects. Elevating the gas knifein this way may reduce disturbance forces. The difference in heightbetween the extractor exit 85 and the first exit 60 a (and the secondexit 60 b) may preferably be greater than or equal to approximately 50μm, or more preferably approximately 100 μm. The difference in heightbetween the extractor exit 85 and the first exit 60 a (and the secondexit 60 b) may preferably be less than or equal to approximately 1000μm, or more preferably approximately 600 μm. The difference in heightbetween the extractor exit 85 and the first exit 60 a (and the secondexit 60 b) may preferably be between approximately 50 μm to 1000 μm, ormore preferably approximately 100 μm to 600 μm.

In any of the above embodiments, a gas supply opening 86 may optionallybe provided to supply gas radially outwards of the gas knife. The gassupply opening 86 is depicted in FIG. 11, but may not be present in FIG.11, or could be present in relation to the description of any of theprevious drawings. The gas supply opening 86 may be configured to supplygas to the area adjacent to the gas knife. The gas supply opening 86 maybe located at the same distance as the gas knife from the surface 90 ofthe substrate W as depicted in FIG. 11. In this way, the gas supplyopening 86 and the exits (i.e. 60 a and 60 b) for the gas knife may beat the same distance from the substrate W as the extractor exit 85, orthe gas supply opening 86 and the exits (i.e. 60 a and 60 b) for the gasknife may be at a different distance to the substrate W than theextractor exit 85. The gas supply opening 86 may be supplied at agreater distance from the substrate than the gas knife. This is notdepicted. This means that a similar step as described above could beprovided between the exits (i.e. 60 a and 60 b) for the gas knife andthe gas supply opening 86. The step may be vertical, angled or curved.

A device manufacturing method may be provided in accordance with any ofthe above embodiments. A method for manufacturing devices may use alithographic apparatus comprising any of the above embodiments. Forexample, a device manufacturing method may comprise a step of projectinga patterned beam of radiation onto a substrate W and the patterned beamof radiation is passed through a region (i.e. a space 11) of immersionfluid. The device manufacturing method may comprise a further step ofconfining the immersion fluid to the region using a fluid handlingstructure 12. The fluid handling structure 12 comprises a gas knifesystem which generates a gas knife radially outward of the region. Thedevice manufacturing method may also comprise a step of using the gasknife system, where the gas knife contributes to the confining step. Thegas knife system comprises a series of passages each having an exit. Thegas knife may be formed by gas exiting the exits. The passages comprisea plurality of first passages 70 a having a plurality of correspondingfirst exits 60 a, and a plurality of second passages 70 b having aplurality of corresponding second exits 60 b. At least one first passageand at least one second passage are configured such that the stagnationpressure of gas exiting the first exit is greater than the stagnationpressure of the gas exiting the second exit, wherein the plurality offirst passages and the plurality of second passages are intermingled andarranged in a line such that the first exits and the second exits form aside of a shape in plan view. The plurality of first passages and theplurality of second passages may form at least one, multiple or all thesides of the shape in plan view.

As described above, it is beneficial to provide a way of reducing orpreventing defects by reducing or preventing bulldozing and/or filmpulling. A fifth embodiment includes an immersion lithographic apparatuscomprising a fluid handling structure 12. The fluid handling structure12 is configured to confine a flow of immersion fluid to a space 11(which may otherwise be referred to as a region). The fluid handlingstructure 12 comprises a gas knife in use. The gas knife may be formedradially outward of the space 11 and may be configured to contribute toconfining the immersion fluid. The fluid handling structure comprisingat least one exit and the gas knife being formed by gas exiting the atleast one exit, wherein the at least one exit is arranged so that thegas knife forms a side of a shape in plan view, wherein the at least oneexit has a geometry configured to allow movement of a droplet ofimmersion fluid from a position radially outward of the gas knife to aposition radially inward of the gas knife and is configured to restrictmovement of a droplet of immersion fluid from a position radially inwardof the gas knife to a position radially outward of the gas knife.

The geometry of the at least one exit forming the side in plan view(forming the gas knife) may therefore be configured to allow movement ofa droplet in one direction, and restrict movement of a droplet inanother direction. The geometry in plan view (i.e. the shape of the sideformed by the at least one exit in plan view) may be configured suchthat when a droplet of immersion fluid approaches the gas knife from aposition radially outward, the geometry may allow movement of thedroplet of immersion fluid to a position radially inward of the gasknife. For example, this may occur when the side is the advancing sideof the fluid handling structure 12. Additionally, the geometry may beconfigured such that when a droplet of immersion fluid approaches thegas knife from a position radially inward, the geometry may restrictmovement of the droplet of immersion fluid to a position radiallyoutward of the gas knife. For example, this may occur when the side isthe receding side of the fluid handling structure 12. Thus, the sameside may control the movement of a droplet of immersion fluid to allowand restrict movement depending on whether the side is the advancingside or the receding side of the fluid handling structure 12. In otherwords, the geometry in plan view may be configured to allow movement ofa droplet of immersion fluid as described when it is the advancing sideof the fluid handling structure 12, but restrict movement of a dropletof immersion fluid as described when it is the receding side of thefluid handling structure 12.

Allowing movement of a droplet of immersion fluid from a positionradially outward of the gas knife to a position radially inward of thegas knife means that if the fluid handling structure 12 approaches adroplet of immersion fluid on the surface of the substrate W, instead ofcolliding with the droplet and pushing the droplet forwards along thesurface of the substrate W (which may cause defects), the droplet maypass through the gas knife into the fluid handling structure 12, thusreducing or preventing the occurrence of defects due to bulldozing.Restricting or preventing movement of a droplet of immersion fluid froma position radially inward of the gas knife to a position radiallyoutward of the gas knife means that less immersion fluid is left on thesurface of the substrate W after the fluid handing structure 12 movesrelative to it such that the occurrence of defects due to film pullingmay be reduced or prevented.

As described above, for previously known apparatus, it is known thatincreasing the stagnation pressure of the gas knife may reduce the filmpulling, however, this can have an adverse effect on bulldozing.Therefore, increase of the stagnation pressure of the gas knife may belimited and a balance of higher stagnation pressure and lower stagnationpressure needs to be reached. The present embodiment may reduce thebulldozing at the advancing side of the fluid handling structure 12 (byallowing droplets to move radially inward) to such an extent that higherstagnation pressure can still be used at the receding side of the fluidhandling structure 12 than could otherwise be implemented withpreviously known apparatus. Therefore, higher stagnation pressure can beprovided and this can reduce film pulling at the receding side of thefluid handling structure 12 whilst minimizing or maintaining bulldozingeffects at the advancing side of the fluid handling structure 12 ascompared to using known apparatus. These advantages can be achieved byproviding one gap 210 on the advancing side (i.e. multiple gaps may beprovided but aren't required) because a single gap on the advancing sidemay reduce bulldozing, and the reduction in bulldozing may allow anincrease in the overall stagnation pressure used for the gas knife suchthat film pulling may be reduced on the receding side due to theincreased stagnation pressure. However, having a geometry with multiplegaps 210 may improve the advantages provided. For example, there is anadvantage to having at least one gap 210 on each side of the shape inplan view such that these advantages can be achieved irrespective of thedirection of movement of the fluid handling structure 12 (i.e. when thefluid handling moves in any direction, there will be a gap 210 on theadvancing side).

The gas knife having the geometry described in the fifth embodiment mayhave the same advantages as the soft and strong jets in the first tofourth embodiment. In more detail, in the first to fourth embodiments,droplets may pass radially inward of the gas knife due to the soft jetson the advancing side, and providing a gap 210 on an advancing side ofthe fluid handling structure 12 would allow movement of a droplet ofimmersion fluid from a position radially outward of the gas knife to aposition radially inward of the gas knife providing the same advantagesrelating to reducing bulldozing. Furthermore, in the first to fourthembodiments, droplets may be prevented from moving radially outward ofthe gas knife by the strong jets on the receding side, and the gas knifecan be at a higher stagnation pressure when gaps 210 are provided asdescribed above which restricts movement of a droplet of immersion fluidfrom a position radially inward of the gas knife to a position radiallyoutward of the gas knife and thus provides the same advantages relatingto reduced film pulling. Furthermore, an advantage of the gap 210 beingprovided using the geometry as herein described is that although the gap210 allows entry of droplets when on the advancing side, the gap 210 canstill prevent or restrict movement of droplets outwards when on thereceding side. Thus, film pulling can be reduced or prevented when thegap 210 is provided on a receding side.

Known fluid handling structures generally have exits wherein gas exitingthe exits form the gas knife. Generally, it is known that a gas knife isformed by exits which are in a straight line or form a continuous shape.In the fifth embodiment, the geometry of the at least one exit (i.e. thegeometry of the side of the shape in plan view) is configured in such away as to provide a layout which allows movement of a droplet ofimmersion fluid from a position radially outward of the gas knife to aposition radially inward of the gas knife and is configured to restrictmovement of a droplet of immersion fluid from a position radially inwardof the gas knife to a position radially outward of the gas knife. Inother words, the configuration of the side in plan view provides thisfunction.

More specifically, the fluid handling structure 12 comprises at leastone exit 200 and the gas knife may be formed by gas exiting the at leastone exit 200. The at least one exit 200 is arranged so that the gasknife forms a shape in plan view, or more specifically, the sides of ashape in plan view. For example, the shape may be similar to the shapedepicted in FIG. 3, and the at least one exit 200 may correspond to theexits 60 depicted in FIG. 3. It is noted that the exits 200 referred toin the fifth embodiment may or may not have passages shaped as describedin relation to the first, second, third and/or fourth embodiments.Either way, the gas knife may form a variety of shapes due to thegeometry of the at least one exit 200.

In the fifth embodiment, a gap 210 may be formed along at least one ofthe sides of the shape in plan view. (This gap is not depicted in FIG.3.) The gap 210 is shown in FIG. 12A. FIG. 12A is a close up of at leasta portion of one of the sides of the shape. For example, FIG. 12A coulddepict a close up of at least a portion of the bottom right hand side ofthe four pointed star shape in FIG. 3, although altered to include a gap210. The gap 210 is configured to allow movement of a droplet ofimmersion fluid from a position radially outward of the gas knife to aposition radially inward of the gas knife. For example, the gap 210 mayprovide an opening where droplets on the surface of the substrate Wwhich collide with the fluid handling structure 12 at the advancing sideof fluid handling structure 12 may pass under the fluid handlingstructure 12 and may enter the space 11. The possible movement of such adroplet is indicated by arrow A2 in FIG. 12A. As the fluid handlingstructure 12 reaches a droplet of immersion fluid which is radiallyoutward of the gas knife, the droplet may move along the edge of the gasknife due to the relative movement and when the droplet reaches the gap210, the droplet may move inwards of the gas knife.

There may be multiple gaps 210 formed along at least one of the sides ofthe shape in plan view. There may be at least one gap 210 on more thanone side. If gaps 210 are formed on other sides, the shape of the atleast one exit 200 at the gap 210 may be mirrored or rotated to providethe same effect at different parts of the gas knife. In an example, theshape formed by the gas knife is a four pointed star as depicted in FIG.3, and there are multiple gaps 210 formed on each side. The number ofgaps 210 on each side may be the same. There may be any number of gaps210 which is practical, for example, there may be 1, 2, 3, 4, 5, 6, 7,8, 9, or more gaps 210 on each side.

When relative movement between the substrate W and the fluid handlingstructure 12 is in a direction such that the side is the advancing sideof the fluid handling structure 12, then a droplet of immersion fluidahead of the side is pushed along the edge of the gas knife, which cancreate defects (i.e. bulldozing). The gap 210 allows the droplet ofimmersion fluid to pass from a position outward of the gas knife to aposition inward of the gas knife to reduce bulldozing. The distancebetween a point where the droplet of immersion fluid reaches the gasknife and the gap 210 which allows the droplet to move inwards is calledthe mean droplet distance. Before passing through the gap 210, themovement of the droplet along the edge of the gas knife may still leadto bulldozing. It may be beneficial to provide multiple gaps 210 alongthe same side. The mean droplet distance may be optimized, i.e., beinglarge enough to catch droplets of immersion fluid, so as to reducebulldozing.

The gap 210 may be between approximately 200 μm to 1000 μm. These areexemplary values and the size of the gap 210 may be selected from anyreasonable value to optimize the likelihood of allowing immersion fluidto enter radially inwards of the gas knife.

At least a portion of the side comprising the gap 210 may comprise twoend portions 220, 230 along that side and the gap 210 may be formedbetween the two end portions 220, 230 of the at least one exit 200. Thetwo end portions 220, 230 may form at least a part of the shape. Out ofthe two end portions, a first end portion 220 may comprise a bend. Thebend may be a curved portion as depicted in FIG. 12A. The first endportion 220 may be configured to restrict movement of a droplet ofimmersion fluid left behind from a position radially inward of the gasknife to a position radially outward of the gas knife at the recedingside of the fluid handling structure 12. The possible movement of such adroplet is indicated by arrow A1 in FIG. 12A. This droplet movement mayoccur when the substrate W is moved relative to the fluid handlingstructure 12 in a direction opposite to a scanning direction, whereinthe scanning direction is depicted by arrow 110 in FIG. 12A. The firstend portion 220 may only be slightly curved, as depicted in FIG. 12A.The first end portion 220 may be more curved and may form a U-shape or ahook shape. The first end portion 220 may be straight, but the end maybe at an angle to the rest of that part of the opening. In other words,the first end portion 220 may comprise a bend between two straightportions.

If there are multiple gaps 210, there may be multiple end portions 220,230, and in particular multiple end portions 220 each comprising a bend.

The first end portion 220 is positioned such that if a droplet ofimmersion fluid is to pass outward from the fluid handling structure 12,the droplet will encounter part of the gas knife and will be collectedin the first end portion 220. The first end portion 220 may eithercollect the droplets of immersion fluid and/or redirect them. The fluidhandling structure 12 may optionally comprise a droplet extractor 240 toremove droplets which have been rounded up by the first end portion 220.The droplet extractor 240 may be the similar to the extractor describedabove in relation to FIG. 3. For example, the droplet extractor 240 maybe a dual phase extractor. Although the droplet extractor 240 isdepicted in FIG. 12A, this is optional and may be provided in furtherdrawings, e.g. FIG. 12B. There may be multiple first end portions 220.There may be the same number of first end portions 220 as there are gaps210.

The other of the two end portions may optionally be a straight endportion 230. This may be advantageous for allowing droplets to enterinwards of the gas knife, for example, following movement A2 in FIG. 12Awhen the substrate W is travelling relative to the fluid handlingstructure 12 in the scanning direction 110. This allows droplets toenter inward of the gas knife at the advancing side of the fluidhandling structure 12.

In the fifth embodiment, when in use, the substrate W may be movedrelative to the fluid handling structure 12 in the scanning direction110. A portion of the shape of at least one opening 200 may overlap withthe other portion of at least one opening 200. For example, in a planeperpendicular to the scanning direction 110, one of the end portions 230or 220 may be positioned to overlap with the other end portion 220 or230. This may mean that there is no gap in a plane perpendicular to thescanning direction 110. In other words, in the scanning direction 110(i.e. if viewed along the scanning direction), there is no gap betweenthe tip of each of the end portions 220 and 230. In other words, in thescanning direction 110, the end portions 220 and 230 overlap with eachother, i.e. if viewed in the scanning direction 110 in FIG. 12A.

Having an overlap, i.e. no gap along the scanning direction 110, meansthat if a droplet is inwards of the gas knife, and the fluid handlingstructure 12 is moving along the scanning direction 110, no matter wherethe droplet is located, it will encounter the gas knife. As long as thesubstrate W moves relative to the fluid handling structure 12 parallelto the scanning direction 110, then droplets are likely to move relativeto the fluid handling structure 12 parallel to the scanning direction110 and would thus reach a part of the gas knife, for example, as formedby the end portions 230 or 220. This helps restrict or even preventmovement of a droplet of immersion fluid from a position radially inwardof the gas knife to a position radially outward of the gas knife.

FIG. 12A depicts the at least one exit 200 as slits. For example, theshape formed by the at least one exit 200 may be a continuous shape withthe gap 210 as depicted in FIG. 12A. The at least one exit 200 may beformed as a slit (i.e. a continuous groove) in the fluid handlingstructure 12 through which gas exits. Alternatively, at least part ofthe gas knife may be formed by gas exiting a plurality of exits. If theat least one opening 200 is formed by a slit, the shape in plan view maybe formed by one continuous slit with a gap 210 being formed on only oneside. Therefore, when the fluid handling structure 12 is oriented suchthat the gap 210 is on an advancing side, the geometry is configured toallow movement of a droplet of immersion fluid radially inward of thegas knife, whereas when the fluid handling structure 12 is oriented suchthat the gap 210 is on a receding side, the geometry is configured torestrict movement of a droplet of immersion fluid radially outward ofthe gas knife. The gap 210 may be formed between a first end of the slitand a second end of a slit. For example, the shape formed by the atleast one exit 200 as a substantially continuous slit may be a rhombus,but along one side of the shape, the gap 210 may be formed between twoends of the slit, such as those depicted in FIG. 12A.

For example, the at least one exit 200 may be many discrete openings asdepicted in FIG. 12B. The gas exits the openings to form the gas knifein the same way as described above. Although the openings are depictedas circular, they could be any shape and this is not particularlylimiting. If the gas knife is formed by a plurality of openings, the gap210 may be wider than the distance between the edges of two adjacentopenings. The gap 210 may be greater than 1 times the distance betweenthe edges of two adjacent openings. The gap may be up to approximately 5times the distance between the edges of two adjacent openings.

In the fifth embodiment, instead of, or as well as providing thegeometry described above, the at least one exit 200 may comprise aplurality of discrete openings and the distance between each of theopenings and the size of each of the openings may be selected and variedin order to allow movement of a droplet of immersion fluid from aposition radially outward of the gas knife to a position radially inwardof the gas knife and is configured to restrict movement of a droplet ofimmersion fluid from a position radially inward of the gas knife to aposition radially outward of the gas knife, e.g., depending on whetherthe side is the advancing side or the receding side of the fluidhandling structure 12. For example, the at least one exit 200 may bereplaced with the first exit 60 a and the second exit 60 b as describedabove.

In the fifth embodiment, as described above, immersion fluid may be leftbehind at the receding side of the fluid handling structure 12 after thefluid handling structure 12 is moved relative to the substrate W.Although varying the stagnation pressure of the gas knife as describedabove may help reduce the immersion fluid left behind, it may bepossible to reduce this further by considering the shear stress exertedon the surface of the immersion fluid.

In the fifth embodiment, the at least one exit 200 is located on asurface of the fluid handling structure 12, which may be similar to thesurface 80 depicted in FIGS. 8 and 9. The surface 80 may be facing andsubstantially parallel to the top surface 90 of the substrate W when inuse as depicted in FIG. 13. The at least one exit 200 may have a majoraxis which passes through the center of the cross-sectional area of theat least one exit 200. The major axis of the at least one exit 200 maybe at an angle to the top surface 90 of the substrate W when in use.This may appear in cross section to be the same as FIG. 10 except thatthe first passage 70 a is replaced with the at least one exit 200. Inother words, the at least one exit 200 may be at an incline. The angle αmay preferably be greater than or equal to approximately 10°, or morepreferably approximately 30°. The angle α may preferably be less than orequal to approximately 75°, or more preferably approximately 60°. Theangle α may preferably be between approximately 10° to 75°, or morepreferably between approximately 30° to 60°.

By providing the at least one exit 200 at an incline, the shear stresson the surface of the immersion fluid may increase and there may be aninflow underneath the at least one exit 200. This inflow may have aninward shear stress (possibly a large inward shear stress) which mayhelp droplets of immersion fluid to pass radially inward in the fluidhandling structure 12 when on the advancing side and maintaining theimmersion fluid radially inward of the gas knife when in use when on thereceding side, i.e., confining the immersion fluid inside the space 11and restricting movement of a droplet of immersion fluid radiallyoutward of the gas knife.

In the fifth embodiment, the fluid handling structure 12 may furthercomprise a fluid extractor radially inward of the gas knife. The fluidextractor may have at least one extractor exit 85. The fluid extractormay be the same as the extractor described in relation to FIG. 3 and theextractor exit 85 may correspond to the openings 50. The extractor exit85 may be on the same surface 80 of the fluid handling structure 12 asthe at least one exit 200. An example is depicted in FIG. 14 which showsa cross-section through the extractor exit 85 and the at least one exit200. As can be seen, this may appear in cross section to be the same asFIG. 11 as described above, except that the first passage 70 a (and thesecond passage 70 b) is replaced with the at least one exit 200. Beingon the same surface 80 means that the extractor exit 85 and the at leastone exit 200 are both on the same side of the fluid handling structure12, for example, a side of the fluid handling structure 12 facing thetop surface 90 of the substrate W in use. The surface 80 may havevariations in height as described below. The surface 80 may provide aconnection between the extractor exit 85 and the first exit 60 a and/orthe second exit 60 b. In other words, the extractor exit 85, the firstexit 60 a and/or the second exit 60 b may be provided on the samesurface 80 which is a continuous surface on one component of the fluidhandling structure 12. The surface 80 of the fluid handling structure 12may be facing and substantially parallel to the top surface 90 of thesubstrate W when in use. There may be a step in the surface 80 such thatthe at least one exit 200 is at a greater distance from the substrate Wthan the extractor exit 85 when in use, i.e. the gas knife is elevated.

The step may be a vertical step as depicted in FIG. 14, or it may beangled, i.e. the difference between the parts of the surface 80 at adifferent height may be angled, i.e. inclined. Alternatively, the stepmay be curved. Varying the height of the at least one exit 200 may alterthe effect of the resulting gas knife on the surface of the substrate Wand may help reduce defects. Elevating the gas knife in this way mayreduce disturbance forces. The difference in height between theextractor exit 85 and the at least one exit 200 may preferably begreater than or equal to approximately 50 μm, or more preferablyapproximately 100 μm. The difference in height between the extractorexit 85 and the at least one exit 200 may preferably be less than orequal to approximately 1000 μm, or more preferably approximately 600 μm.The difference in height between the extractor exit 85 and the at leastone exit 200 may preferably be between approximately 50 μm to 1000 μm,or more preferably approximately 100 μm to 600 μm.

In the fifth embodiment, a gas supply opening 86 may optionally beprovided to supply gas radially outwards of the gas knife. A gas supplyopening 86 may be provided outward of the gas knife. The gas supplyopening 86 may or may not be provided with any variation of the fifthembodiment. The gas supply opening 86 may be configured to supply gas tothe area adjacent to the gas knife. The gas supply opening 86 may belocated at the same distance as the gas knife from the top surface 90 ofthe substrate W as depicted in FIG. 14. As can be seen, FIG. 14 issubstantially the same as FIG. 11 as described above, except that thefirst passage 70 a (and the second passage 70 b) is replaced with the atleast one exit 200. In this way, the gas supply opening 86 and the atleast one exit 200 may be at the same distance from the substrate W asthe extractor exit 85, or the gas supply opening 86 and the at least oneexit 200 may be at a different distance to the substrate W than theextractor exit 85. The gas supply opening 86 may be supplied at agreater distance from the substrate W than the gas knife. This is notdepicted. This means that a similar step as described above could beprovided between the at least one exit 200 and the gas supply opening86. The step may be vertical, angled or curved.

A device manufacturing method may be provided in accordance with thefifth embodiment. A method for manufacturing devices may use alithographic apparatus comprising any variation relating to the fifthembodiment. For example, a device manufacturing method may compriseprojecting a patterned beam of radiation onto a substrate, wherein thepatterned beam of radiation is passed through a region of immersionfluid, confining the immersion fluid to the region using a fluidhandling structure of an immersion system, wherein the fluid handlingstructure comprises a gas knife system, and generating a gas kniferadially outward of the region, using the gas knife system, wherein thegas knife contributes to the confining step, and the fluid handlingstructure comprising at least one exit and the gas knife being formed bygas exiting the at least one exit, wherein the at least one exit isarranged so that the gas knife forms sides of a shape in plan view,wherein the at least one exit has a geometry configured to allowmovement of a droplet of immersion fluid from a position radiallyoutward of the gas knife to a position radially inward of the gas knifeand configured to restrict movement of a droplet of immersion fluid froma position radially inward of the gas knife to a position radiallyoutward of the gas knife.

A further device manufacturing method may comprise projecting apatterned beam of radiation onto a substrate, wherein the patterned beamof radiation is passed through a region of immersion fluid, confiningthe immersion fluid to the region using a fluid handling structure of animmersion system, wherein the fluid handling structure comprises a gasknife system, and generating a gas knife radially outward of the region,wherein the fluid handling structure comprises at least one exit, the atleast one exit being arranged so as to form the gas knife forming a sideof a shape in plan view wherein the side comprises two end portionsalong that side and a gap is formed between the two end portions alongthat side of the shape in plan view, and one of the end portionscomprising bent end portion, and wherein in use, a substrate is movedrelative to the fluid handling structure in a scanning direction, andthe shape overlaps with itself such that the gap is not visible in aplane perpendicular the scanning direction.

It is noted that any variation of the fifth embodiment may be used incombination with any variation described above, and in particular, withany of the first, second, third and/or fourth embodiments. For example,the first exit 60 a and the second exit 60 b may be used to provide theat least one exit 200.

In any of the above embodiments, at least one additional gas outlet 300may be provided as depicted in FIG. 15. FIG. 15 is the same as FIG. 3except for the multiple additional gas outlets 300. The at least oneadditional gas outlet 300 may be provided with any of the abovedescribed embodiments, for example with any of the first to fourthembodiments as will be described herein. The at least one additional gasoutlet 300 may be located between the meniscus controlling feature (asdepicted by the discrete openings 50 in FIG. 15) and the gas knife. Inrelation to the first to fourth embodiments, this may be between themeniscus controlling feature and the exits 60. In this context the word“between” means radially outward of the meniscus controlling feature,and radially inward of the exits 60.

As previously described, the substrate W may be moved relative to thefluid handling structure 12, immersion fluid may be dragged behind thefluid handling structure 12, e.g., at the receding side of the fluidhandling structure 12. When the meniscus of the immersion fluid breaksover the surface of the substrate W, a fluid film is left on thesubstrate W. The film retracts over the whole length of atrailing/receding side of the fluid handling structure 12. Theretracting film will break up into droplets on substrate W in atriangular pattern. The trailing side(s) may be any side of the fluidhandling structure 12 depending on the relative movement of thesubstrate W. The trailing side may be changed if the direction ofrelative movement between the substrate W and the fluid handlingstructure 12 is changed. These immersion fluid droplets may lead towatermark defects as described above. However, it has been found thatproviding dry spots along the length of the trailing side of the fluidhandling structure 12 may help reduce the watermark defects resultingfrom the retraction of the immersion fluid film.

As mentioned, the at least one additional gas outlet 300 may be used toprovide gas between the meniscus controlling feature and the gas knife.The additional gas outlet 300 may be a discrete opening used to providegas. For example, the gas provided by the at least one additional gasoutlet 300 may be CO₂ gas. The gas may be provided to create local dryspots along the length of a trailing side of the fluid handlingstructure 12. The stagnation pressure of gas exiting the additional gasoutlet 300 may be approximately the same as, or greater than, thestagnation pressure of gas exiting the exits 60 forming the gas knife inuse.

By creating or promoting dry spots, the film may be broken up intosmaller, separate films along the length of the trailing side of thefluid handling structure 12. The smaller, separate films may retractfrom several positions along the length of the trailing side of thefluid handling structure 12 rather than retracting over the full lengthof the trailing side of the fluid handling structure 12. Retracting inseveral smaller portions may result in the droplets forming smallerretraction triangular patterns on the surface of the substrate W. Thismay therefore decrease the overall amount of immersion fluid and/or thenumber of droplets left on the surface of the substrate W. In otherwords, the overall amount of immersion fluid in the smaller triangularpatterns is less than it would otherwise be if a larger triangularpattern of droplets was formed from the film retracting along the entirelength of the trailing side of the fluid handling structure 12. Thus,the at least one additional gas outlet 300 may be provided to promotedrying spots between the meniscus controlling feature and the gas knifeto reduce immersion fluid left on the substrate W.

It may be possible to create this effect using only one additionaloutlet 300. For example, placing one additional gas outlet 300 along thetrailing side of the fluid handling structure 12 may mean that theimmersion fluid retracts in two separate film portions rather than one.The additional gas outlet 300 may preferably be located to separate thelength of the trailing side of the fluid handling structure 12 intoequal portions. For example, an additional gas outlet 300 may beprovided in an approximately central location along the trailing side ofthe fluid handling structure 12. Alternatively, more than one additionalgas outlet 300 may be provided. For example, one additional gas outlet300 on multiple sides, or per side, of the fluid handling structure 12may be provided. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 etc. or up to 50 or evenmore additional gas outlets 300 may be provided on at least one,multiple or all sides. There may be different numbers of additional gasoutlets 300 on different sides of the fluid handling structure 12, or atleast two sides may have the same number of additional gas outlets 300as each other. The number of additional gas outlets 300 is notparticularly limiting, and any appropriate number may be used. Having alarger number of additional gas outlets 300 means that the amount ofimmersion fluid left behind on the substrate W may be further reducedand the area over which the remaining immersion fluid is left behind onthe substrate W may be located towards the outer edge of the substrateW.

The pitch may be determined as the distance from the center of oneadditional gas outlet 300 to the center of an adjacent additional gasoutlet 300. This is likely to be determined along a single side of thefluid handling structure 12. The pitch may be between approximately 20to 100 times larger than the pitch between adjacent exits 60. The pitchmay be greater than or equal to approximately 1 mm. The maximum pitchmay be defined by the length of a side of the fluid handling structure12 in which only one additional gas outlet 300 is provided. In otherwords, if only one additional gas outlet 300 is provided along one side,the maximum pitch is not greater than the length of one side. As anexample, if the additional gas outlet 300 is provided in the middle of aside, the pitch will be half the length of the side. Additionally, thelength of the film pulling time will decrease as the number ofadditional gas outlets 300 are provided along the trailing side. Thefilm pulling time may be the time during which the gas knife loses waterdroplets outward onto the substrate W. This stops when the fluid startsto retract between the gas knife and the meniscus controlling feature.The pitch may be selected depending on estimated or measured formationof immersion fluid droplets on the surface of the substrate W.

Although not depicted, at least one additional gas outlet 300 may beprovided with the fifth embodiment. This may be substantially the sameas described above except that the additional gas outlet 300 may beprovided between the extractor exit 85 (which may correspond to themeniscus controlling feature) and the at least one exit 200 (to replacethe exits 60 described above). In this context the word “between” meansradially outward of the meniscus controlling feature, and radiallyinward of the at least one exit 200.

In an embodiment, there is provided an immersion lithographic apparatuscomprising a fluid handling structure, the fluid handling structureconfigured to confine immersion fluid to a region and comprising a gasknife system, the gas knife system comprising passages each having anexit, the passages comprising a plurality of first passages having aplurality of corresponding first exits, and a plurality of secondpassages having a plurality of corresponding second exits, wherein atleast one first passage and at least one second passage are configuredsuch that the stagnation pressure of gas exiting the first exit isgreater than the stagnation pressure of gas exiting the second exit, andthe plurality of first passages and the plurality of second passages areintermingled and arranged in a line such that the first exits and thesecond exits form a side of a shape in plan view.

In an embodiment, the at least one first passage has a first entranceand the at least one second passage has a second entrance and a firstratio is the ratio of the corresponding first exit to the firstentrance, and a second ratio is the ratio of the corresponding secondexit to the second entrance, and the second ratio is larger than thefirst ratio. In an embodiment, the cross-sectional area of the firstexit is approximately equal to or less than the cross-sectional area ofthe corresponding first entrance and the cross-sectional area of thesecond exits is approximately equal to or larger than thecross-sectional area of the corresponding second entrance. In anembodiment, the cross-sectional area of the second passage increasesmonotonically from the second entrance to the second exit. In anembodiment, the second passage forms a frustum shape from the secondentrance to the second exit. In an embodiment, the angle of sides of thesecond passage to a major axis through the passage is betweenapproximately 0.5° and 7°. In an embodiment, the second passagecomprises a first portion having a substantially uniform cross-sectionalarea along the length of the first portion, and a second portion havinga substantially uniform cross-sectional area along the length of thesecond portion, wherein the second portion has a larger cross-sectionalarea than the first portion. In an embodiment, the first passage has thefirst entrance and the second passage has the second entrance and thefirst entrance has a larger cross-sectional area than the first exit andthe second exit has approximately the same cross-sectional area as thesecond entrance. In an embodiment, the cross-sectional area of the firstpassage decreases monotonically from the first entrance to the firstexit. In an embodiment, the first passage forms a frustum shape from thefirst exit to the first entrance. In an embodiment, the angle of sidesof the second passage to a major axis through the passage is betweenapproximately 0.5° and 30°, or more preferably, between approximately0.5° and 10°. In an embodiment, the first passage comprises a firstportion having a substantially uniform cross-sectional area along thelength of the first portion, and a second portion having a substantiallyuniform cross-sectional area along the length of the second portion,wherein the second portion has a larger cross-sectional area than thefirst portion. In an embodiment, the first exit and the second exit arelocated on a surface of the fluid handling structure, the surface facingand being substantially parallel to a top surface of a substrate when inuse, and the first passage has a first major axis which passes throughthe center of the cross-sectional area of the first entrance and firstexit and the second passage has a second major axis which passes throughthe center of the cross-sectional area of the second entrance and secondexit, wherein the first major axis and/or the second major axis is at anangle to the top surface of a substrate when in use, wherein the angleis preferably between approximately 10° to 75°, or more preferablybetween approximately 30° to 60°. In an embodiment, the fluid handlingstructure further comprises a fluid extractor radially inward of the gasknife, the fluid extractor having an extractor exit on a surface of thefluid handling structure as the first exit and the second exit, thesurface facing and being substantially parallel to a top surface of asubstrate when in use, wherein there is a step in the surface such thatthe first exit and the second exit are at a greater distance from thesubstrate than the extractor exit when in use.

In an embodiment, there is provided a device manufacturing methodcomprising: projecting a patterned beam of radiation onto a substrate,wherein the patterned beam of radiation is passed through a region ofimmersion fluid; confining the immersion fluid to the region using afluid handling structure, wherein the fluid handling structure comprisesa gas knife system; and generating a gas knife radially outward of theregion, using the gas knife system, wherein the gas knife contributes tothe confining step, and wherein the gas knife system comprises passageseach having an exit, the passages comprising a plurality of firstpassages having a plurality of corresponding first exits, and aplurality of second passages having a plurality of corresponding secondexits, wherein at least one first passage and at least one secondpassage are configured such that the stagnation pressure of gas exitingthe first exit is greater than the stagnation pressure of gas exitingthe second exit, and the plurality of first passages and the pluralityof second passages are intermingled and arranged in a line such that thefirst exits and the second exits form a side of a shape in plan view.

Although specific reference may be made in this text to the use oflithographic apparatus in the manufacture of integrated circuits, itshould be understood that the lithographic apparatus described hereinmay have other applications, such as the manufacture of integratedoptical systems, guidance and detection patterns for magnetic domainmemories, flat-panel displays, liquid-crystal displays (LCDs), thin-filmmagnetic heads, etc. The skilled artisan will appreciate that, in thecontext of such alternative applications, any use of the terms “wafer”or “die” herein may be considered as synonymous with the more generalterms “substrate” or “target portion”, respectively. The substrate Wreferred to herein may be processed, before or after exposure, in forexample a track (a tool that typically applies a layer of resist to asubstrate W and develops the exposed resist), a metrology tool and/or aninspection tool. Where applicable, the disclosure herein may be appliedto such and other substrate processing tools. Further, the substrate Wmay be processed more than once, for example in order to create amulti-layer integrated circuit, so that the term substrate W used hereinmay also refer to a substrate W that already contains multiple processedlayers.

In any of the embodiments, the gas used for the gas knife and/orsupplied by the gas supply opening may be ay suitable gas. Optimally,the gas comprises CO₂, or is pure CO₂.

The terms “radiation” and “beam” used herein encompass all types ofelectromagnetic radiation, including ultraviolet (UV) radiation (e.g.having a wavelength of or about 365, 248, 193, 157 or 126 nm). The term“lens”, where the context allows, may refer to any one or combination ofvarious types of optical components, including refractive and reflectiveoptical components.

While specific embodiments of the invention have been described above,it will be appreciated that the invention may be practiced otherwisethan as described.

One or more embodiments of the invention may be used in a devicemanufacturing method.

A liquid supply system as contemplated herein should be broadlyconstrued. In certain embodiments, it may be a mechanism or combinationof structures that provides a liquid to a space between the projectionsystem and the substrate and/or substrate table. It may comprise acombination of one or more structures, one or more fluid openingsincluding one or more liquid openings, one or more gas openings or oneor more openings for dual phase flow. The openings may each be an inletinto the immersion space (or an outlet from a fluid handling structure)or an outlet out of the immersion space (or an inlet into the fluidhandling structure). In an embodiment, a surface of the space may be aportion of the substrate and/or substrate table, or a surface of thespace may completely cover a surface of the substrate and/or substratetable, or the space may envelop the substrate and/or substrate table.The liquid supply system may optionally further include one or moreelements to control the position, quantity, quality, shape, flow rate orany other features of the liquid.

The descriptions above are intended to be illustrative, not limiting.Thus, it will be apparent to one skilled in the art that modificationsmay be made to the invention as described without departing from thescope of the claims set out below.

1. A fluid handling structure for an immersion lithographic apparatus,the fluid handling structure configured to confine immersion fluid to aregion and comprising: a gas knife system comprising passages eachhaving an exit, the passages comprising: a plurality of first passageshaving a plurality of corresponding first exits, and a plurality ofsecond passages having a plurality of corresponding second exits,wherein at least one first passage and at least one second passage areconfigured such that the stagnation pressure of gas exiting the firstexit is greater than the stagnation pressure of gas exiting the secondexit, and the plurality of first passages and the plurality of secondpassages are intermingled and arranged in a line such that the firstexits and the second exits form a side of a shape in plan view.
 2. Thefluid handling structure of claim 1, wherein the at least one firstpassage has a first entrance and the at least one second passage has asecond entrance and a first ratio is the ratio of the correspondingfirst exit to the first entrance, and a second ratio is the ratio of thecorresponding second exit to the second entrance, and the second ratiois larger than the first ratio.
 3. The fluid handling structure of claim2, wherein the cross-sectional area of the first exit is approximatelyequal to or less than the cross-sectional area of the correspondingfirst entrance and the cross-sectional area of the second exits isapproximately equal to or larger than the cross-sectional area of thecorresponding second entrance.
 4. The fluid handling structure of claim3, wherein the cross-sectional area of the second passage increasesmonotonically from the second entrance to the second exit.
 5. The fluidhandling structure of claim 3, wherein the second passage forms afrustum shape from the second entrance to the second exit.
 6. The fluidhandling structure of claim 3, wherein the angle of sides of the secondpassage to a major axis through the passage is between approximately0.5° and 7°.
 7. The fluid handling structure of claim 3, wherein thesecond passage comprises a first portion having a substantially uniformcross-sectional area along the length of the first portion, and a secondportion having a substantially uniform cross-sectional area along thelength of the second portion, wherein the second portion has a largercross-sectional area than the first portion.
 8. The fluid handlingstructure of claim 2, wherein the first passage has the first entranceand the second passage has the second entrance and the first entrancehas a larger cross-sectional area than the first exit and the secondexit has approximately the same cross-sectional area as the secondentrance.
 9. The fluid handling structure of claim 8, wherein thecross-sectional area of the first passage decreases monotonically fromthe first entrance to the first exit.
 10. The fluid handling structureof claim 8, wherein the first passage forms a frustum shape from thefirst exit to the first entrance.
 11. The fluid handling structure ofclaim 8, wherein the angle of sides of the second passage to a majoraxis through the passage is between approximately 0.5° and 30°.
 12. Thefluid handling structure of claim 8, wherein the first passage comprisesa first portion having a substantially uniform cross-sectional areaalong the length of the first portion, and a second portion having asubstantially uniform cross-sectional area along the length of thesecond portion, wherein the second portion has a larger cross-sectionalarea than the first portion.
 13. The fluid handling structure of claim1, wherein the first exit and the second exit are located on a surfaceof the fluid handling structure, the surface facing and beingsubstantially parallel to a top surface of a substrate when in use, andthe first passage has a first major axis which passes through the centerof the cross-sectional area of the first entrance and first exit and thesecond passage has a second major axis which passes through the centerof the cross-sectional area of the second entrance and second exit,wherein the first major axis and/or the second major axis is at an angleto the top surface of a substrate when in use, and wherein the angle isbetween approximately 10° to 75°.
 14. The fluid handling structure ofclaim 1, further comprising a fluid extractor radially inward of the gasknife, the fluid extractor having an extractor exit on a surface of thefluid handling structure as the first exit and the second exit, thesurface facing and being substantially parallel to a top surface of asubstrate when in use, wherein there is a step in the surface such thatthe first exit and the second exit are at a greater distance from thesubstrate than the extractor exit when in use.
 15. A devicemanufacturing method comprising: projecting a patterned beam ofradiation onto a substrate, wherein the patterned beam of radiation ispassed through a region of immersion fluid; confining the immersionfluid to the region using a fluid handling structure, wherein the fluidhandling structure comprises a gas knife system; and generating a gasknife radially outward of the region, using the gas knife system,wherein the gas knife contributes to the confining step, and wherein thegas knife system comprises passages each having an exit, the passagescomprising a plurality of first passages having a plurality ofcorresponding first exits, and a plurality of second passages having aplurality of corresponding second exits, wherein at least one firstpassage and at least one second passage are configured such that thestagnation pressure of gas exiting the first exit is greater than thestagnation pressure of gas exiting the second exit, and the plurality offirst passages and the plurality of second passages are intermingled andarranged in a line such that the first exits and the second exits form aside of a shape in plan view.